Today's telephony users generally have at least one wireline-based telephone receiving services through the public switched telephone network (PSTN) and a mobile telephone receiving services through a cellular network. These wireline and mobile telephones are incompatible, and are thus incapable of facilitating communications over both the cellular and public switched networks. As such, telephony users must juggle multiple telephones, using one telephone to make and receive calls via the cellular network, and another to make and receive calls via the PSTN. Given the multiple telephones, callers must keep track of multiple directory numbers. Additionally, incoming calls are generally free through the service providers of the PSTN, while cellular service providers charge for such incoming calls. Accordingly, there is a need for a technique to allow a single telephony device to interface with both the cellular network and the PSTN in an effective and efficient manner.
Given the increase in packet-based voice calls and the movement toward using packet networks to support calls normally supported by the PSTN over packet networks, there is a need to for a technique to allow a single telephony device to interface with both the cellular network and a packet network. Given the inherent mobility associated with mobile telephones, there is also a need to provide an efficient transfer mechanism to transition a call through the cellular network to a call through the PSTN or packet network, when communications via the PSTN or packet network are desired or necessary.